Britain's National parks - enjoyed by 100 million visitors a year - must undergo a conservation revolution if they are to meet the challenges of climate change and the introduction of new farming practices.

This is the stark warning of leading environmentalist Adrian Phillips, who has warned the National Parks Societies that our most precious landscapes will have to adapt in the near future. Phillips wants planners to encourage small renewable energy projects, such as wind turbines, hydroelectric schemes and solar water heaters. He warned that new planning laws will have to be introduced to make new buildings carbon-neutral and the parks entirely so.

Traditional farming would be wound down in marginal areas while some landscapes should be 're-wilded' to absorb more water and reduce flooding downstream. Peat bogs, which can store carbon, must be conserved and restored.

A former director-general of the Countryside Commission, which was subsumed into the Countryside Agency in 1999, Phillips worked for the World Conservation Union and is a professor of countryside and environmental planning at Cardiff University. He is also a trustee of the National Trust and sits on a plethora of crucial bodies.

He said: 'The impact of climate change in national parks is going to be even greater than anyone has foreseen. No one is arguing that we get rid of national parks. Far from it. But the forces are so large that the traditional approach is not enough.'

Phillips's views are controversial: 'Global warming is making it very difficult for upland farmers to survive. Some will ... but the idea that we can keep the great part of our national parks farmed full-time in the future is unrealistic.' In five years, he said, most National Trust hill farms in the Lake District will be losing money.

Instead of preserving traditional farming practices at all costs, Britain's uplands must provide a range of environmental services for the whole nation, he argued. They must act as a buffer from the effects of global warming, absorbing increased rainfall to reduce flooding, protecting biodiversity and reducing the UK's carbon emissions by restoring the nation's peat bogs. Farmers or land managers should be paid for those services.

'We have this double problem of too much water followed by too little water,' said Phillips. 'The management of uplands will help deal with some of that, holding as much water as you can for as long as you can in the uplands. Man-made drainage systems installed to improve the land for livestock would be removed, making the land wetter. It would maintain its peaty capacity where huge amounts of carbon are locked up.'

Phillips knows his message won't be welcomed everywhere. 'There's a deep cultural resistance to the idea of land no longer being farmed, but it has other values which are now probably much higher for society. If asked if they want change, people will say no.

'But there would be so many benefits from a wilder form of landscape that it would become accepted. It requires political leadership. That's why I worry because local park communities are quite resistant to those changes. It's pretty alien.'

However, Phillips has found an ally in the new chief executive of the Lake District National Park, Richard Leafe. 'The landscape has always changed to reflect the climate or the issues of the day,' Leafe said. 'The Lakes has been an industrial mining area, it's been heavily logged for charcoal, and I see the climate agenda as the next expression of that process of change. I'm confident that communities here are ready for that change in a way that other communities might not be.' Leafe also wants to see micro-renewable energy projects installed in his park: 'In the Lake District 100 years ago there were 20 hydroelectric schemes, but there are only six now. We have locations like Langdale where micro-renewable wind turbines would work alongside a farm.

'We've got to get a grip of the carbon resources here. There's more carbon in the peat bogs of England than there is in all the forests of the United Kingdom and France put together. If we did one thing it should be to reduce the rate of loss of peat through erosion and turn that around.' In the Peak District, a project called Moors for the Future is already restoring peat bogs ravaged by pollution and over-grazing.

That change is happening, Leafe said, because formerly conservative land agencies - such as water authorities that own large parts of the parks - are changing fast. 'That's making a huge difference,' he explained. 'United Utilities realise there's a real bonus for them to focus on management because it helps reduce the amount of treatment they have to put in the water when it comes out of the reservoirs. It's the same with the National Trust. They are showing fantastic leadership in the climate-change debate.'

The government also seems to have woken up to the conservation value of national parks. Despite deep cuts in the government budget planned in the medium term, Rural Affairs Minister Jonathan Shaw announced last week that funding for national parks would increase by 10 per cent over the next three years, marginally above inflation.

A showcase for how Britain's national parks could develop in the future already exists in Cumbria. Ennerdale runs east to west about 10 miles from the coast. In 2000 the National Trust and the Forestry Commission agreed to try a new method of management in a valley degraded by inappropriate conifer plantations.

The idea was to allow natural processes a much greater say in how the valley changed. Two years later the third major landholder in the area, United Utilities, joined the project. The valley wasn't abandoned, but managed at a lower level of intensity. Sheep are being replaced by fewer, larger herbivores such as Black Galloway cattle and red deer. Wardens monitor the cattle via satellite to track their movements but they calve alone and are allowed to roam freely.

Leafe argued that building this 'ecological resilience' is the idea to reinvigorate national parks not just naturally, but socially too: 'This process takes farmers, and that means communities, shops and post offices and all those things. Otherwise we'll end up with a ghetto where only the rich live and the people who look after the place and make it thrive travel in great distances by car to do it.'

Park life by numbers

12 Percentage of Earth's surface covered by national parks.

6,555 Number of national parks worldwide. 14 of them are in the UK.

1951 The year the Peak District became the first national park in the UK.

25 Percentage of Britain's threatened birds, animals and plants whose home is the Cairngorms National Park.

2012 The year by which the National Park Authorities organisation is committed to making its own operations carbon neutral.

1810 The year William Wordsworth described the Lake District as a 'sort of national property in which every man has a right and interest who has an eye to perceive and a heart to enjoy'.

42,200 Number of inhabitants in the Lake District, the most populated national park in the UK.